What are communication satellites?
There was a time when man used to communicate by beating drums or burning fires. Those days, in the absence of any scientific knowledge, it was extremely difficult to send messages to distant places. Today, we have different means of communication like the telephone, radio, television and the press. Now scientists have added artificial communication satellites or comsats to send telephone, radio, telex, fax messages and television signals around the world.
An artificial satellite is a man-made Moon that orbits around the Earth. With the help of rockets, they are launched into geostationary orbits. This means that they are placed in fixed orbits over the equator about 36,000 km high where they orbit the Earth in exactly 24 hours. Because of this they appear to remain stationary in the sky from the Earth. Artificial satellites are of many different shapes and sizes and are sent into orbit for several different reasons. They usually have solar cells which convert the energy of the Sun into electricity which is used to run the satellite instruments.
Communication satellites pick up the signals transmitted from a point on the Earth and relay them to the other side of the world by amplifying them and then beaming them down to a ground station. Communication satellites have different channels for telephone, radio and television signals. The signal is first sent to the satellite with the help of high-frequency microwaves. This is received by the antenna fitted in the satellite. After amplifying, it is transmitted by a transmitter. Its power is increased by a transponder. The signal is received by the earth station. This is how a signal travels thousands of kilometres. If a message is sent through conventional methods, very long cables are required. Today, telephone messages between several countries are exchanged through satellites.
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